Flaxseeds are typically flat, oval, and pointed at one end. They contain a seed coating and an embryo comprising two large, flattened cotyledons, a short hypocotyl and a radical. The seed coating (or hull) of flaxseeds is formed from the ovule and has five hull layers, two of which are considered important. These two hull layers are the epidermal layer, commonly called the mucilage layer, and the testa that consists of pigmented cells, which determine the seed's coloring.
Typically, various abrasion methods have been implemented in dehulling flaxseeds. The oil of flaxseeds may be separated by pressing or extracting it from the whole grain. Flaxseeds have been cultivated in Canada and the USA primarily for oil. The solid residue has been typically used as an animal feed.
Full fat milled seed typically refers to flaxseeds milled by any suitable milling process including grinding and impact techniques where the whole seed is milled without any prior extraction of oil or other components. Defatted flax meal refers to flax meal made from flaxseeds from which oil has been extracted therefrom.
One of the major benefits of processing flaxseeds into a nutritional supplement for humans is that they naturally contain a lignan portion in an amount of roughly 0.7 percent up to 1.5 percent. The primary lignan of flaxseeds is secoisolariciresinol diglycoside (SDG), which is found in a concentration of up to about 1.5 weight percent based on the total weight of the flaxseed. Plant lignans are believed to hold special pharmaceutical benefits inasmuch as they are reported to exhibit broad biological activities, including antitumor, antioxidant, antiviral and estrogenic and antiestrogenic activities. The lignans are generally cinnamic acid dimers containing a dibenzylbutane skeleton. Another benefit of consuming flaxseeds is that they are a rich source of essential fatty acids. It is believed that a daily human consumption of 250 mg of lignan are required to produce some of the beneficial health effects listed above. This, however, equates to the consumption of about 25 g of flaxseed per day, which is an impractical and prohibitive amount for normal daily intake.
With respect to the processing of lignans from flaxseeds, a large portion of the lignans are contained in the flaxseed hulls. Previous efforts for recovering lignans from flaxseeds have included physical abrasion of the flaxseeds to remove a portion of the hulls. It is believed that hull recovery processes that incorporate only dry fractionation have not been able to recover SDG lignans in amounts exceeding roughly 3 weight percent of the total weight of the resultant purified flax product. Other methods of recovering SDG lignans include chemical extraction of the lignans from the flaxseed hulls, which can recover SDG in amounts of up to 95 weight percent of the total weight of the resultant purified flax product. A well known problem, however, of using chemical-type extractions involves the use of environmentally damaging solvents, or more expensive solvents or measures to ensure that dangerous solvents are not released and are properly disposed of.
One previous method involving the dehulling of flaxseeds discloses physically separating hull from its embryo layer by removing moisture upon heating or other drying methods. In particular, Canadian Patent No. 2,167,951 to Cui et al. discloses that flaxseed without drying was not suitable for the dehulling process and that separation of the hull layer from the embryo upon heat treatment was essential for flaxseed to be dehulled mechanically. U.S. Patent Application No. 2003/0131737 to Cui et al. further teaches the drying of flaxseed to reduce the moisture content to about 1 percent or less before being introduced to a separation chamber for abrasive processing.
Thus, it is still desired to provide for flaxseed hull recovery processes that increase the amount of hull recovered.